DE2648900A1 - Microporous chemically resistant carbon articles - made by heating phenolic fabric laminate to high temp. in non-oxidising atmos. - Google Patents

Abstract

Carbon articles are made from stacked or wound layers of (primarily) cellulose which are impregnated with thermosetting resin, cured under pressure to flat or curved sheets, and heated to >800 degrees C in a non-oxidising atmos. The laminated material used is specifically phenolic or cresol resin-impregnated cotton fabric. Process produces thick-walled articles if required, having micro-porosity and without blistering, it uses common raw material, prods. are suitable for e.g. crucibles, conductors, temp.-resistant thermal insulation, filters, prostheses, electrodes because of their chemical and thermal resistance etc.

Description

Process for the production of carbon bodies

The invention relates to a method for the production of carbon bodies, in the case of the body, made up of several stacked or wound on top of each other Layers of predominantly cellulose with a curable polymer Fabric impregnated and cured under pressure, flat or curved surface structures are heated to a temperature> 8000C in a non-oxidizing atmosphere will.

The carbon bodies produced in this way are suitable i.a. for heating pipes or coils for resistance heated furnaces, for crucibles and boats, e.g. for melting chemically aggressive substances, as well as for pipes and plates for lining of containers and apparatus.

In a method described in DT-OS 21 04 680, as Cardboard, cardboard, chipboard and plywood panels, predominantly made of cellulose, e.g. plates made of filter cardboard or cardboard tubes are used. When using cardboard or cardboard essentially correspond to the process steps before carbonization the known working method for the production of hard paper - with the remarkable Deviation that a relatively low pressure of about 1 to 30 during curing kp / cm2 is applied. In conventional hard paper production there are pressing pressures common when hardening 100 kp / cm2 and more. Furthermore, according to DT-OS 21 04 680 particularly resin-rich raw materials are used (resin absorption approx. 400% by weight), while the resin content in commercially available hard paper is 30 to 50.

If you heat a body made of commercially available hard paper that consists of several Layers of paper impregnated with phenolic resin and cured under pressure or just as such cardboard exists, in a non-oxidizing atmosphere with that in the DT-OS 21 04 680 specified speed from about 5 to 100C to 800 to 12000C, so the bodies inflate interlaminar and are practically no longer usable.

The invention is based on the object of having thick-walled molded parts Defined microporosity without generating the aforementioned swelling.

According to the invention, this object is achieved by a method as described at the outset mentioned type solved, with the hard tissue based on phenolic resin or cresol resin and Cotton fabrics are heated.

The starting material for the process according to the invention is are preferably commercial products, e.g. in Saechtling-Zebrowski 1tKunstst # ff # TaschenbÜöh1I. 19. Aufs.

Munich-Vienna 1974, pages 417 to 419, and plate 76, are described. Of course, it is also possible to use hard tissue bodies if necessary produces itself with a composition that is not customary in the trade. It is surprising in that that the fading observed during the carbonisation of hard paper during the carbonisation Hard tissue does not occur as hard paper and hard tissue under the joint Designation '1Schichtpreßstoffe "are summarized (~ 1Kunststoff-Taschenbuch" a. a. 0.).

The starting material for the process according to the invention is therefore a certain group of laminates are used, namely hard tissue, the consist essentially of phenolic or cresol resins reinforced with cotton fabrics. Depending on the proportion of resin components and fabric components as well as depending on the type of resin and fabric fineness, there are commercially available hard fabrics with different properties and qualities (see e.g.

~ Plastic pocket book "loc. Cit.). Hard tissue is available as laminate in the form of plates and as ## ickellaminate in the form of rods and tubes. The starting material is therefore a composite material, which consists essentially of a phenolic resin matrix reinforced with cotton fabrics. Such a composite can also be referred to as a rhenolic resin laminate.

Upon closer examination, it has been shown that, in particular, commercially available Hard tissue often show more or less pronounced inhomogeneities in their structure. These are preferably characterized by areas of greater or lesser resin content. They can be brought about arbitrarily by, for example, at the top and / or bottom web of fabric in the manufacture of laminate panels (Top layer) more heavily impregnated with resin than the other (inner) sheets in this way a smooth, dense, generally better, e.g. more handsome, To achieve surface. - Another unintended inhomogeneity comes into the Starting material in that the impregnated or to be impregnated Fabric panels themselves are faulty, wrinkled and in places very different resin impregnations demonstrate. These manufacturing-related inhomogeneities are referred to below as Harzneseer designated. The described conditions of inhomogeneity as a result of locally increased Resin concentrations in the raw material for manufacture and properties of the carbon material according to the invention have considerable consequences. So judges Among other things, the rate of carbonization depends on whether you have a starting material with density, i.e.

Has resin-rich outer layers or whether there are thick resin pockets in the material occurrence. The pickling speeds given below generally apply, however, in each case the existence of inhomogeneities of the described Kind to be respected.

The heating, i.e. carbonization, of the hard tissue body is preferred Done as follows: The bodies are first placed in a nitrogen atmosphere or in a vacuum at a rate between 10C / h and 500C / h up to 8000C heated, then cooled to room temperature within 1 to 10 hours and then in a vacuum of 10 1 to 10 -3 mm Hg in 1 to 10 hours to at least 16000C heated. - It should be noted that the within the previously specified Ranges of heating and cooling speeds to be selected depending on the wall thickness the body depend - in the sense that larger ### and strength lower ones Require speeds.

If the starting material used according to the invention is subjected to a such defined temperature-time treatment in an inert atmosphere or in a vacuum, this is obtained after reaching a temperature of at least 800 ° C. and more Cooling a product that mainly consists of elemental carbon. A subsequent treatment up to 16000 ° C, in some cases up to 2000 ° C and higher, below Vacuum (about 10 -3 mm Hg) has the consequence that impurities, but in particular also residual hydrogen, are expelled.

It eats known from the procedure in solid-state pyrolysis, that the volatile pyrolysis products formed by thermal decomposition over Diffusion processes have to leave the treated body. In the preparation of of vitreous carbon is a volume diffusion in which the outdiffusion the decomposition products take place particularly slowly. This means that, for example with wall thicknesses of the starting material of around 5 mm, carbonization times of several 100 h up to 1000 h are necessary. In practice, this results in a maximum Layer thickness of vitreous carbon of about 3 mm.

It has now surprisingly been found that the invention When using phenolic resin laminates, the carbonation was carried out much faster can be, although this starting material with specific gravity of 1.3 Up to 1.4 g cm 3 and completely dense packing comparable with unfilled phenolic resins should be. The strongly deviating carbonization behavior can be explained as follows be: When pyrolytic decomposition starts after reaching a certain temperature from about 280 to 300 0C will diffuse from the kome coming from the phenolic resin Decomposition products are strongly favored along the embedded tissue threads. These Type of surface diffusion will increase in intensity very quickly as the Cotton is relatively more degraded (higher weight loss than phenolic resin) and as a result, real channels are created. The initial volume and grain boundary diffusion so goes very early, i.e.

at the beginning of the thermal degradation, in the "fast" pore diffusion above. The practical importance of this pyrolysis mechanism is that once Pyrolysis cycles and post-treatment cycles can be made much shorter or, which is actually synonymous, that much greater wall thicknesses are possible are. The carbonization cycle for a ME-material with a wall thickness of 100 mm requires about the same amount of time as the preparation of a piece of massive vitreous Coal with a wall thickness of 3 mm.

The product of the method according to the invention is a fine-pored carbon body with the crystalline or

paracrystalline habit of vitreous carbon. This novel Material is the product of solid-state pyrolysis.

Closer examination of the final product shows that a carbon body with very fine, regular pores.

In addition to this "primary" porosity, there is also a secondary, which is caused by the fibrillar fine structure of the tissue storage. The qualitative The described process of the diffusion process allows the conclusion that even greater Wall thicknesses than the 100 mm mentioned can be carbonized in a reasonable time can.

A rough calculation shows that the volume of a "primary Single pore of the order of 10 cm3. In the carbonization of the novel For materials up to 16000C, a linear shrinkage of 20 to 30% occurs. The one in this The resulting weight loss range is 60 to 65%. The shrinkage and weight loss values correspond to specific weights of the end product of about 1.00 to 1.40 g cm-3. This is about 45 to 60% of the theoretical density of graphite. The total pore volume so is 40 to 55%. With the value given above for the volume of a primary Single pore results in an average number of pores per unit volume of about 0.5 ~ 106 Pores / cm³.

The latter values characterize the new material in characteristic way. In a sense, it closes the gap between the known macroporous foam (glass-like carbon foam, see e.g. DT-OS 24 53 204) with densities of 0.1 to 1.0 g cm 3 and the massive glassy carbon with densities of 1.45 to 1.55 g cm 3.

X-ray analysis shows that the new material is up to amorphous or paracrystalline at treatment temperatures of 23000C how is glassy carbon. Accordingly, its hardness, abrasion resistance and mechanical strength relatively high (compressive strength> 104 N / cm2). - Of the The coefficient of thermal conductivity is 1 to 3 ~ 10 -2 cal grd 1cm 1s 1 der specific electrical resistance at 1.2 to 1.6 10 2> ^ cm.

In particular, the above-mentioned surface or top layers on a number of physical properties. You surrender generally greater surface hardness, strength, etc. when carbonized Material. The influence on the permeability of the material is also particularly strong for liquids and gases. So when measurements on material with a "dense" surface Permeability coefficients for air of 10-3 to 10-4 cm / s found. Alone through Sanding the "dense" surfaces increases the permeability by about a factor 100 to 10 -2 to 10 -4 cm2 / s.

It has also been found that it is useful even with the mechanical Processing of the form bodies made of layered fabric, the "embossed" in the base material Anisotropy must be taken into account. For example, it is tubular or cylindrical Bodies behave differently during carbonization (more favorable heating rates are possible) as well as different properties in the carbonized final state have, depending on whether you have it from the laminate with the cylinder axis perpendicular, has worked out parallel or in an undefined position to the layering. - The consideration This anisotropy inherent in the material can be optimally used in preparation, depending on the use be used, both in terms of properties and in terms of Carbonation behavior. So it is expedient to become a body before heating work out of the hard tissue in such a way that the position of the tissue layers within the body is matched to the desired properties of the carbon body.

The inventive method has the advantage that one easy can use raw material that is available because it is commercially available. Furthermore it is It is advantageous that very thick-walled parts can be produced with it. on the other hand is the production of very thin-walled ones because of the high mechanical strength Molded parts possible. The raw material can be machined very easily. Machining with hard material tools is limited for the carbonized material Dimensions possible. Preparatory preparatory work, such as when making the glass-like carbon foams are not required.

Possible uses for the carbon-carbon composite material produced according to the invention are e.g .: a) crucible and container material due to chemical inactivity and high abrasion resistance as an alternative to graphite crucibles b) heating conductors because of the relatively high specific resistance c) high temperature resistant thermal insulation because of low specific heat conduction d) Mechanically stable construction material of low specific weight e) Prosthetic material for veterinary and human medicine because of the immunobiological indifference to tissue f) Fine-pored, corrosion-resistant Filters for liquids and gases (acids and vapors) g) electrodes.

The invention is based on a drawing and some exemplary embodiments explained in more detail. In the drawing, FIGS. 1 a, 1 b and 1 c show molded bodies from the to carbonizing starting material, Fig. 2a and 2b two procedures, fort body from the Working out laminate, Fig. 3 is a scanning electron microscope Photo of the carbon composite material produced according to the invention, enlargement about 55 times, Fig. 4 is a diagram in the temperature-time cycles of a carbonization a 15 mm thick hard tissue panel are shown schematically, Fig. 5 is a diagram, in which the dependence of the Aufheizgea speeds from the shortest diffusion path (= half the wall thickness) is applied.

In Fig. 1a is a solid rod and in Fig. Ib a tube made of wound Hard tissue shown, in Fig. 1c a plate made of laminated material.

In Figures 2a and 2b is indicated by dashed lines, like a molded body 1 to be carbonized from a block 2 of laminate, can be worked out e.g. by punching, cutting, sawing or milling, namely the S5gtetriachesese 3 of the molded body in Fig. 2a is perpendicular and Fig. 2b parallel to the layering of the laminate.

In Fig. 3, the structure of the original cotton fabric is still to recognize. The recording shows that it is in the case of the one produced according to the invention Material is a composite body.

In FIG. 4, the temperature 2 (3in 0C is plotted against the time t in hours. With 4 there is a carbonization cycle in an inert gas, e.g. nitrogen, and with 5 denotes a post-treatment cycle (for cleaning) in a vacuum.

In relation to FIG. 5, let us first consider the term "shortest diffusion length" how explained as follows: For bodies of high symmetry, i.e. spheres, cube, cylinders, cuboid Plate, etc., is generally the geometric dimension for the drain of the diffusion process, which is the shortest distance from one in the middle of the given body volume describes the point to the surface. This is So, for example, half the wire diameter for a wire, for a plate half the plate thickness, etc. The longer this characteristic path, the slower it is the temperature must be increased during the carbonization.

In FIG. 5, the hatched area shows the range of the heating speed At% / At as a function of the shortest diffusion path δ (in mm). The one through the hatched The range of variation indicated in the area includes approximately all commercially available starting materials.

Example 1 For the production of an acid-resistant filter disc, from Cut a round disc 80 mm in diameter through a hard tissue board 10 mm thick Sawing and turning produced by machining.

The more resinous outer layers of the starting material are through Twist off a layer 1 mm thick. The resulting round body of about 8 mm thick is then degreased in a solvent, e.g. ethanol / acetone.

The carbonation then takes place. In a 1st carbonation cycle the body is in a nitrogen atmosphere at a rate of about 4 ° C / h brought to a temperature of 800 0C and then within 3 to 4 hours cooled to room temperature, the body has now essentially already achieved the desired Shape and the desired properties.

To remove residual impurities and to stabilize the The carbon body obtained is followed by a second temperature treatment in vacuo. This is done by the body in one Vacuum furnace at a pressure of about 10 -3 mm Hg brought to a temperature of 160,000 within 20 hours and then cooled to room temperature in 16 hours.

The end product is a microporous disc with a density of 1.15 g cm 3. The thickness is 7.8 mm, the diameter 60 mm. The permeability to air was false at around 5 ~ 10 cm2 / s.

Example 2 For the production of a heating conductor from the inventive Material becomes a man-shaped body from a 5 mm thick hard tissue board with a total length of 1250 mm with a bar width of 10 mm by sawing and Milling worked out. -This meander then becomes the one described in example 1 Subjected to carbonation and post-treatment cycles. The carbonization was however with a temperature increase of 10 ° C / h to 80,000, the aftertreatment with 100 ° C / h carried out until 160000.

The end product is a meander made of abrasion-resistant, porous carbon, which in the longitudinal dimensions a linear shrinkage of about 28%, in the thickness, i.e. perpendicular to the stratification, has experienced 20%. The electrical resistance per cm of length is around 0.03 # with a total of 2.8 #. (There were in the same way by appropriately dimensioning resistance elements up to about 15 #) Example 3 Made from a solid rod 100 mm in diameter A crucible was made by turning and grinding the wound hard tissue.

The raw crucible had an outer diameter of 95 mm, an inner diameter of 81 mm, a wall thickness of 7 mm and a floor thickness of 10 mm with an external height of 140 mm. The carbonization was done by heating to 80,000 in 150 hours Aftercare by heating in a vacuum of 10 -3 to 10-2 mm Hg to 16000C in 24 hours carried out.

A microporous carbon crucible was obtained as the end product, its dimensions - about 75 mm outer diameter, 63 mm inner diameter, inner height 103 mm and total height 110 mm - correspond to a linear shrinkage of 21 to 22%. The density of the crucible material is 1.12 g cm-3.

Example 4 rods made of hard tissue with dimensions 4. 4 66 mm3 were in flowing nitrogen in a heating-cooling cycle with linear time Temperature profile heated to different temperatures. In the area of the Transition "polymer carbon" occurs in the temperature range from 500 to 7000C a particularly strong change in resistance (to the course of the specific Resistance as a function of the treatment temperature of vitreous carbon see Fig. 5 in Chemie Ing. Techn. 42 (1970) No. 9/10, pp. 659-669). It was there possible, through targeted partial carbonization, test resistances in the range from 100 moles to 1 # and smaller. For the chopsticks of the above Dimensions were obtained by heating resistors to temperatures between 550 and 720 0C realized between 5 M # and 1 #. The duration of the heating cycles was in each case 1000 minutes.

The table below gives measured values of physical properties Kolilenstoffkörper produced according to the invention put together.

- Table - TABLE Bending strength 3) 210 to 320 kg / cm2 1) 440 to 520 kg / cm 2) 1040 to 1430 kg / cm 1) Compressive Strength 3) 1040 to 1430 kg / cm22 1240 to 1830 kg / cm 2) Special electrical resistance 12 to 16. 10-3 #cm Permeability for air 10-2 to 10-4 cm2 / s up to 10-7 cm / s clear 1.1 to 1.4 g / cm3 j) Treated up to 8000C 2) Treated up to 16000C 3) The lower values of the strength apply to measurements perpendicular to the stratification, the higher values for measurements parallel to the stratification.

Patent claims:

Claims (3)

Claims: 1. Process for the production of carbon bodies, in the case of the body, made up of several stacked or wound on top of each other Layers of predominantly cellulose with a curable polymer Fabric impregnated and cured under pressure, flat or curved surfaces consist in a non-oxidizing atmosphere at a temperature> 8000C, characterized in that hard tissue based on phenolic resin or cresol resin and cotton fabric are heated. 2. The method according to claim 1, characterized in that d # aß before Heat body out of the hard tissue in such a way that the position the tissue layers within the body to the desired properties of the carbon body is matched. 3. The method according to claim 1 or 2, characterized in that the Body first in a nitrogen atmosphere or in a vacuum at one speed heated between 1 ° C / h and 500C / h up to 8000C, then within 1 to 10 hours cooled to room temperature and then in a vacuum of 10 1 to 10 3 mm Hg can be heated to at least 16000C in 1 to 10 hours.